1. Field of the Invention
The present invention relates to a shower head, a thin film-manufacturing device and a method for manufacturing a thin film.
2. Description of the Related Art
In the conventional thin film-manufacturing device, in particular, such a device equipped with a mechanism for elevating or ascending and descending a substrate-supporting stage, the stage is moved or pulled along the exhaust direction upon the evacuation of the device (film-forming vessel) due to the play of the elevating mechanism and this accordingly leads to the loss of the balance of a concentric exhaust port (a path for evacuation) about the stage, which has been adjusted in advance under the atmospheric pressure. For this reason, in order to ensure a uniform film thickness distribution, it is necessary to use an exhaust port having a diameter of not less than 5 mm for the deviation of ±3% in the film thickness and a diameter of not less than 10 mm for the deviation of ±2% therein (see, for instance, WO 03/048413 A1 (Page 18; FIG. 8)). Moreover, such a device equipped with a mechanism for elevating a substrate-supporting stage should be so designed that it secures a large space (for instance, 3 L) below the substrate-supporting stage during the film-forming stage in order to elevate the stage from its substrate-transporting position to its film-forming position. This lower space is one for realizing the required isotropic evacuation, but the stage is pulled along the exhaust direction upon the evacuation of the device due to the play of the elevating mechanism as has been discussed above and this in turn leads to the loss of the balance of the concentric exhaust port, which has been adjusted in advance under the atmospheric pressure. Therefore, it has been needed to secure a space larger than that usually required.
There has also been known a device provided with a deposition-inhibitory plate for preventing any film-formation on the inner wall of the film-forming vessel. This device has a deposition-inhibitory plate-elevating mechanism for elevating the plate upon the film-formation and for letting it down upon the transfer of the substrate. In this case, however, a film-forming gas simply flows through the vessel during the film-forming step and therefore, a film is formed on the inner wall of the deposition-inhibitory plate, which constitutes the reaction space. This becomes a source of particles and this in turn shortens the maintenance cycle of the mass-production device.
In the case of the device equipped with the above deposition-inhibitory plate, the film-forming gas also passes around behind the outer wall of the plate, and a film is little by little formed even on the inner wall of the film-forming vessel. In the case of the device free of any deposition-inhibitory plate, a film is directly formed on the inner wall of the film-forming vessel. When the film is formed on the inner wall of the vessel up to a critical thickness, it is peeled off from the wall and this accordingly serves as a source of particles.
If the temperature of a shower head for introducing a film-forming gas into a reaction chamber is controlled in a conventional thin film-manufacturing device, the distance between the shower head and a substrate should be adjusted depending on the kinds of substrates and starting materials selected. However, a shower nozzle is a movable part (see, for instance, Japanese Un-Examined Patent Publication Hei 9-316644 (Claims, Examples)) and therefore, an unnecessary space is formed around the shower head and convection or a turbulent flow may be generated therein. This also serves as a source of particles and in turn makes the maintenance cycle of the mass-production device short.
In such a thin film-manufacturing device which requires the use of such temperature control, it is in general that the distance between the surface of the shower head (or shower plate) and a substrate is set at a level of not more than 40 mm and that the shower head is cooled by the circulation of an oil in an environment in which the surface of the shower head is extremely heated by radiation. However, there has not yet been developed any structure which permits the satisfactory dissipation of heat from the surface of the shower head or the satisfactory heat-exchange. For this reason, it has been needed to reduce the temperature of the circulated oil to an extremely low level. In this case, the temperature of the parts other than the shower head surface is reduced to a lower level even if the temperature of the shower head surface is controlled to an optimum level. This in turn results in the deposition of raw materials and becomes a cause of particle generation.
Regarding the device in which the foregoing temperature control is carried out, the strength of aluminum (Al) begins to cause an abrupt reduction in an environment in which the temperature of a cooling medium exceeds 120° C. and therefore, the passage of the cooling medium should presently be produced from such a material as SUS in consideration of safety. As has been well known in the art, SUS is highly inferior in the heat conduction (the heat conductivity of SUS is about 16 W/mK, while that of Al is about 240 W/mK) and it is thus quite insusceptible to heat transfer. For this reason, when the shower head surface is a separate plate-like part in the shower head structure whose parts constituting the passage of the cooling medium are produced from SUS, the separate plate-like part should be so designed that the heat-exchanging area between the plate and the parts constituting the passage is sufficiently large and the passage of the cooling medium is arranged in the proximity to the contact surface of the plate, for the improvement of the heat-exchange efficiency of the plate.
Moreover, in a conventional thin film-manufacturing device, quartz or alumina which is excellent in the heat resistance has been used as a material for preparing substrate-stage members which come in close contact with a heat source. However, alumina is insufficient in the thermal shock properties. Accordingly, there is observed an increase in the frequency of crack generation or breakage due to the ascent and descent of each substrate. In addition, the quartz is opacified and/or deteriorated due to the loss of O2 in a reducing reaction atmosphere maintained at a high temperature and the film-forming environment for the substrate is thus changed. These phenomena may also serve as sources of particles. As a result, various problems arise such that the maintenance cycle of the device is shortened and that the device never permits any stable film-formation over a long period of time.
Furthermore, if the interior of the conventional thin film-manufacturing device is vented, the vent is conducted upwardly or from the lower space towards the upper space. Therefore, the vent is accompanied by the fling up of the particles generated during the formation of the film and accordingly, the interior of the reaction chamber should be cleaned for every vent. As disclosed in, for instance, an earlier patent application filed by the instant applicant or Japanese Patent Appln. Ser. No. 2003-61391, the number of particles as determined on the substrate increases even when stopping the gas supply between the substrate processing lots. For this reason, there has been desired for the development of a system which permits the down flow vent subsequent to the down flow state of the device without interruption of any gas supply.
The foregoing conventional devices are not designed in due consideration of any turbulent flow, convection and/or heat convection possibly encountered when letting a gas flow and they are quite liable to cause peeling off of the film during film-formation and to generate particles.
When the film formed on, for instance, the inner wall of the film-forming vessel is cleaned up as has been discussed above and the film is not efficiently removed through the reactions with, for instance, a plasma or a gaseous chemical, such cleaning must directly be conducted by an operator using a chemical such as nitric acid, but such operation is quite dangerous. Alternatively, it is sometimes necessary to use a large-scaled operation as another cleaning method, in which the film-forming vessel is dismantled or removed from the device, transported to a cleaning maker and cleaned therein. Consequently, such a thin film-manufacturing device is not practical as a mass-production type device which should highly safely and efficiently be used.